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groups of polymer matrix, which collectively
result in a quite strong nanofiller-matrix interface181. Acid-purified nanodiamonds was exhibit to
improve mechanical properties of another common biodegradable polymer,
poly-(methyl methacrylate) (PMMA) which is used, for example in dental
implants. The introduction of the acid-purified nanodiamonds in concentrations
as small as 0.1 wt.% resulted in increased strength and fracture toughness of
PMMA. At 0.8 wt.% nanodiamonds content, Young’s modulus was 80% higher and the
Tg increased by 20 °C182. Similar to PVA, the developed properties are
described by hydrogen bonding between the polymer carbonyl groups and ND OH
groups. TEM micrographs of the ND–PMMA nanocomposites indicate significant agglomeration
of nanodiamonds, suggesting that further advancement are possible when well
dispersed single ND particles become available183. Polycarbonate (PC) and PMMA were reinforced
with as-received and different functionalized nanodiamonds. Hardness and
Young’s modulus of these nanocomposites were increased by up to 100%, when the
appropriate surface functionality was selected. The largest improvements in
mechanical properties were obtained by using amide functionalized nanodiamonds
for PMMA and amino-functionalized nanodiamonds
for PC emphasize the importance of nanodiamonds surface chemistry in designing
the interface to different matrices184. It is worth mentioning that in many cases it
is difficult to disentangle the contributions of nanodiamonds surface chemistry
into improved nanodiamonds –matrix interface and better nanodiamonds dispersion
in the matrix, which normally interpret into a larger volume of the interphase.
Judiciously chosen surface chemistry is often advantageous for both, resulting
in a stronger interface, while at the same time maximizing the interphase185. Poly-Lactic Acid (PLA) is a well-known
biodegradable polymer used in tissue engineering. Storage modulus, tensile
modulus, and the tensile strength of PLA were enhanced by the addition of 5
wt.% nanodiamonds. The reasons for the improvements might be due to the
increased crystallinity of the matrix (measured by DSC) as well as the
attractive molecular interactions between nanodiamonds and PLA molecules as
suggested by the increased thermal stability of the composite measured in TGA.
An enantiomer of PLA, poly-L-(Lactic-Acid) (PLLA), 

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